Hyperthermia (HT) is a cancer treatment that utilizes heat to destroy cancerous tumors. The past two decades have offered new advances in HT to varying degrees of success. Although HT is still an experimental treatment in the United States and is usually only applied to late-stage cancer patients, international HT results from various countries give more promise to this treatment. The major arguments for local and regional HT result from patients with locally advanced malignancies, where increased response and survival rates have been shown using HT combined with radiotherapy in phase-III trials as compared to radiation alone.
Technical problems still exist regarding different HT approaches, therapeutic potential, and evidence of effectiveness. The foremost problem is generally related to generating and controlling the temperature applied to the tumors and the surrounding tissue. A sufficiently high temperature is needed for inducing programmed cell death (apoptosis) of the tumor cells, but too high a temperature is known to cause neighboring normal cells to undergo necrosis, or otherwise become damaged. The currently accepted target window of temperatures for HT is between about 42° C. and 45° C., with 43° C. considered to be the ideal temperature for apoptosis of tumor cells without harming neighboring normal cells.
To address HT control problems, various methods have been utilized to localize HT heating and limit its temperatures through various applicators, materials, and procedures. One method has been to implant ferromagnetic materials into the human body proximate to tumor sites to cause the ferromagnetic particles to heat up responsive to an externally applied magnetic field. This process is known as interstitial HT (IHT) as it uses interstitial particles or related ferromagnetic thermoseeds. The ferromagnetic material generally comprises particles such as iron oxide or various nickel compounds.
The use of interstitial particles has been extensively researched, with results as early as 1971 using thermally self-regulating implants to produce brain lesions. This method is particularly useful for delivering thermal energy to deep seated tumors. These implants have been shown to heat surrounding tissue until they reach a Curie temperature at which heating is no longer produced. However, most ferromagnetic (FM) materials are toxic even in low concentrations and quite soft and thus require a biocompatible encapsulating coating layer. Unfortunately, the coating layer can adversely efficacy of procedure. Moreover, FM particles are generally non-biodegradable and thus either remain in the treatment location or require a difficult removal process.